Ancient origin of animal U-box ubiquitin ligases

<p>Abstract</p> <p>Background</p> <p>The patterns of emergence and diversification of the families of ubiquitin ligases provide insights about the evolution of the eukaryotic ubiquitination system. U-box ubiquitin ligases (UULs) are proteins characterized by containing a peculiar protein domain known as U box. In this study, the origin of the animal UUL genes is described.</p> <p>Results</p> <p>Phylogenetic and structural data indicate that six of the seven main UUL-encoding genes found in humans (<it>UBE4A</it>, <it>UBE4B</it>, <it>UIP5</it>, <it>PRP19</it>, <it>CHIP </it>and <it>CYC4</it>) were already present in the ancestor of all current metazoans and the seventh (<it>WDSUB1</it>) is found in placozoans, cnidarians and bilaterians. The fact that only 4 - 5 genes orthologous to the human ones are present in the choanoflagellate <it>Monosiga brevicollis </it>suggests that several animal-specific cooptions of the U box to generate new genes occurred. Significantly, <it>Monosiga </it>contains five additional UUL genes that are not present in animals. One of them is also present in distantly-related protozoans. Along animal evolution, losses of UUL-encoding genes are rare, except in nematodes, which lack three of them. These general patterns are highly congruent with those found for other two families (RBR, HECT) of ubiquitin ligases.</p> <p>Conclusions</p> <p>Finding that the patterns of emergence, diversification and loss of three unrelated families of ubiquitin ligases (RBR, HECT and U-box) are parallel indicates that there are underlying, linage-specific evolutionary forces shaping the complexity of the animal ubiquitin system.</p>

Abstract licence: CC BY

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